1. Field of the Invention
The invention relates to a fastener driving tool and, more particularly, to a fastener driving tool which includes replaceable wear surfaces which provide for three point support of the tool on its side to protect the handle casting and the magazine housing. Other features of the invention include reducing the manufacturing costs and improving the ergonomic appeal of such fastener driving tools. Additionally, an improved fastener feed system allows for feeding collated fasteners with relatively large fastener heads which heretofore have caused misoperation of the tool due to inadequate clearance.
2. Background of the Invention
Certain external surfaces on fastener driving tools are subject to wear due to the work habits of the users, particularly when such tools are used in roofing applications. More particularly, users have been known to pick the tool up by way of the external pneumatic hose. Due to the abrasiveness of the roofing material and the weight of the tool, this causes the tool to be dragged across the roofing surface which, in turn, can cause excessive wear on the handle casting and the magazine housing of the tool. Replacement of such items is relatively expensive. Moreover, this requires the roofing installer to have either backup tools available or to complete the installation with a hammer.
Some manufacturers of fastener driving tools have addressed this problem by providing wear surfaces which allow for two point support of the tool on its side. For example, as shown in FIGS. 1 and 2, a known fastener driving tool 20 is shown with wear guards 22 on the magazine housing 24. Such wear guards consist of a U-shaped metal clip as illustrated in FIG. 3. Such clips 22 are clamped against the walls of the magazine housing 24 at diametrically opposite points as shown.
By placement of the U-shaped clips 22 on the magazine housing 24, two point support of the tool 20 is provided. One point of support is the clip 22 as shown in FIG. 2. The other point of support, identified with the reference numeral 26, is the handle casting 28. Although the wear guards 22 provide some protection against wear of the magazine housing 24 when the tool 20 is dragged across a roofing surface, no protection of the handle casting 28 is provided.
Moreover, there are disadvantages in using the U-shaped clips 22 for the magazine housing 24. With such a design, the magazine housing 24 must be opened to replace the U-shaped clips 22. Also, the U-shaped clip 22 may move from its desired location while the tool 20 is being dragged across the surface of the roof. Moreover, with such a design, the clip 22 may be installed in the wrong location and thus allow wear on the magazine housing 24.
In other known fastener driving tools, an elongated L-shaped wear guard 30 (FIG. 4) is provided on the handle casting 28 at the point of contact. More particularly, one leg 32 of the wear guard 30 is attached to the handle casting 28, while the other leg 34 acts as the wear surface. However, in such a design no protection is provided for the magazine housing 24. Moreover, the elongated L-shaped wear guard 30 can cause other problems. More particularly, such a wear guard 30 can cause the contact surface on the depending leg 34 to be worn away resulting in a relatively sharp surface on the remaining leg 32. This can potentially become a user hazard.
There are various other problems associated with known fastener driving tools. These problems relate to: reducing the overall manufacturing costs of the tool; improving the ergonomic appeal of the tool; and improving fastener feed assemblies for collated fasteners with relatively large fastener heads.
Regarding manufacturing costs, there are several identifiable areas which result in relatively high manufacturing costs. These areas include: first, the lack of standardization of handle castings for tools with different power requirements; and second, the relatively tight tolerances required for components within the drive cylinder assembly within the handle casting.
Regarding the first mentioned problem, it is known that the driving force supplied by a fastener driving tool to a fastener head is a function of the respective volumes of the air reservoir and the trapped air chamber within the handle casting. These volumes are controlled, in part, by the size of the handle casting. Consequently, tools with different driving force requirements utilize different size handle castings. Since handle castings are a relatively significant part of the overall tool cost, this results in fastener driving tools that are relatively expensive to manufacture.
As previously mentioned, the relatively tight tolerance requirements of components in the drive assembly can also result in relatively high manufacturing costs. More specifically, the drive assembly includes a reciprocally mounted piston to which a fastener driver or ram is attached disposed within a drive cylinder. The drive cylinder is positioned within the handle casting and closed by a poppet valve disposed adjacent a top cap. Since axial movement of the drive cylinder within the handle casting must be minimized, if not eliminated, the components must be machined to relatively tight tolerances, for example 0.010 inch. Such components can significantly increase the overall manufacturing cost of the tool.
Various ergonomic features of known fastener driving tools affect the acceptance of the tools by end users. One feature relates to the overall tool profile. Tools with relatively large profiles tend to be less desirable by potential end users. This problem is exacerbated when mufflers 36 are added to the tools. In such a situation, the mufflers are often located in the handle casting top cap 38 as shown in FIG. 5. As shown in FIG. 5, the height of the top cap 38 is significantly increased by the amount indicated as H.sub.1 to accommodate the muffler 36. The increased height of the top cap 38 significantly increases the profile of the tool making the tool less attractive to potential purchasers and end users.
Another factor which affects the overall ergonomic desirability of a tool is the location of the exhaust discharge. As shown in FIG. 5, known fastener driving tools are provided with a muffler 36 on the top portion of the top cap which allows for radial discharge of the exhaust through exhaust ports, identified with the reference numeral 40. Many end users prefer that the exhaust be discharged downwardly from the front portion of the tool in the direction of the arrow identified with the reference numeral 42 in FIG. 11.
Other known fastener driving tools without a muffler are provided with an exhaust port 44 in the top cap 38 which allows the exhaust to be discharged in the direction of the arrow 46. The direction of exhaust discharge in both top caps illustrated in FIGS. 5 and 6 make such tools relatively less desirable from an ergonomic standpoint.
Lastly, there are problems with certain known fastener feed assemblies 48, as shown in FIG. 7, normally utilized with relatively low density collated fasteners 50 as shown in FIG. 8. When such fastener feed assemblies are utilized with relatively high density collated fasteners 52 with relatively large diameter fastener heads, such as shown in FIG. 9, certain problems can occur; for example, misoperation of the tool and nail jams.
Such high density collated fasteners generally consist of a web 54 and upper and lower tabs 56 and 58, respectively, with fastener receiving openings 60 for removably receiving fastener shanks 62. In the case of particular fasteners 64 with relatively large diameter head portions 66, such as roofing nails, the fastener heads can interfere with the drive assembly 48 and cause misoperation of the tool. More particularly, known fastener feed systems as illustrated in FIG. 7 and described in U.S. Pat. No. 4,383,608, generally include a feed pawl 68 which feeds from an indexing opening 70 just behind the fastener 62 to be driven as shown in FIG. 7. However, due to the lack of adequate clearance between the fastener head 66 and the web 54, the upper tab 56 folds down on top of the feed pawl 68 during a fastener driving operation which, in turn, interferes with the axial alignment of the fastener 62 with respect to the driver blade. This, in turn, causes the driver blade to strike the fastener head 66 at a position other than its center, possibly causing the fastener to become jammed within the fastener feed assembly 48.